This invention relates generally to a workpiece surface finishing machine, and more particularly to an improved barrel finishing machine having a dual barrel structure with linings and stopper means provided inside the lining of a rotary container of the dual barrel structure for restraining deformation of the lining due to thermal expansion or the like.
The barrel finishing machine generally comprises a dual barrel structure having a cylindrical stationary container and a rotary container concentrically provided in the stationary container with a small gap therebetween. Inner walls of the stationary and rotary containers are covered by linings formed from urethane, rubber or the like.
In the above-described barrel finishing machine, the rotary container is driven so that toroidal flow of an abrasive media and workpieces is caused in the dual barrel structure, thereby finish-processing the workpieces. A mixture of the abrasive media and workpieces will hereinafter be referred to as "mass." The temperature of the mass becomes higher under the influence of frictional heat produced during a finishing operation. The mass temperature is raised to approximately 100.degree. C. in an extreme case. Such temperature rise in the mass causes the lining of the dual barrel structure to thermally expand. As the result of the thermal expansion, the diameter of the lining covering the inner surface of the rotary container is increased. Increase in the diameter of the lining is also caused by the weight of the mass or the centrifugal force due to rotation of the rotary container. The size of the gap between the stationary and rotary containers is reduced with the increase in the lining diameter, and may cause seizure between the rotary container and the lining of the stationary container. The gap between the stationary and rotary containers needs to be small to prevent galling due to the invasion of abrasive media or the like into the gap. Therefore, the gap cannot be enlarged in to accommodate thermal expansion of the lining.
Measures to prevent expansion of the diameter of the lining covering the inner surface of the rotary container are disclosed by Japanese Laid-open (kokai) Utility Model Registration Application Nos. 48-74392 (1973) and 62-29248 (1987), for example. FIGS. 3 and 4 illustrate these measures respectively.
Referring to FIG. 3, a stopper edge 51 is formed integrally with a base 50a (steel) so as to project therefrom at a position slightly inside the outer circumferential edge of a rotary container 50 over the entire circumference thereof. The stopper edge 51 is provided to serve as a weir against thermal expansion of a lining 52 in the outer circumferential direction. On the other hand, in FIG. 4, the stopper edge 51' is formed integrally with the rotary container 50' so as to rise from the outer circumferential edge of the container and be directly opposite to the lining 54' covering the inner surface of the stationary container 53'. Each above-described construction can provide an effective restriction of the expansive deformation of the lining.
Although the foregoing problem resulting from thermal expansion of the lining can be solved by each above-described prior art construction, each construction gives rise to a new problem.
Even the linings of the dual barrel structure are gradually abraded during the finishing operation. Accordingly, the head portion of the stopper edge 51, 51' becomes exposed as the lining wears over time. In many cases, the head portion of the stopper edge 51, 51' is not actually exposed. Rather the stopper edge 51, 51' becomes frequently chipped over most of its length. Once the stopper edge 51, 51' is worn, it ceases serving as a weir against the expansive deformation of the lining. When the container is relined, all the components of the rotary container including the base 50a, 50a' to be replaced with new ones since the stopper edge 51, 51' is integral with the base 50a, 50a'. Consequently, repair work is time consuming and the costs of repair are relatively high. Furthermore, in the prior art, the service life of the lining 52, 52' is limited to a range S of the depth from the surface to the head portion of the stopper edge 51, as shown in FIG. 3. Thus, the cycle time period between required relinings is short. Additionally, since wear of the stopper edge 51 requires replacement of an overall rotary container, the degree of wear of the stopper edge 51 needs to be strictly monitored, which necessitates a troublesome check.
Furthermore, when only the rotary container is replaced with a new one in relining the rotary barrel, a step is formed between the worn-out portion of the stationary container, and a sliding face of the rotary container and the step forms a dead space during the finishing operation, which exerts a bad influence upon the finishing. Consequently, the stationary container also needs to be replaced with a new one even if it is not worn much.